Nonlinear effects in locally resonant nanostrip phononic metasurface at GHz frequencies

In this paper, we report on the observation of nonlinear effects in a nanostrip phononic metasurface (NPM) that enable tuning resonance frequencies at 1.42 GHz. The NPM resonator made periodic array is fabricated lithium niobate substrate. Each nanostrips 250 nm wide and 680-nm-thick SiO2 layer stacking 50-nm Al metal electrodes. Finite element analysis reveals device operates vertically polarized (compression) mode with substantial acoustic energy confined nanostrips, leading to local low velocity. Due nonlinearity, frequency decreases increase stimulation power. underlying mechanism nonlinearity found be power-dependent coupling adjacent nanostrips. This induces softening substrate surface region, which reduces velocity and, hence, bulk radiation. As result, quality factor improve demonstrates reliable method for realization metasurfaces, would significantly enrich mechanisms manipulation waves high frequencies.